Nuclear thermionic generator with composite particle cathode

ABSTRACT

This invention relates to the art of generating power and has particular relationship to thermionic generators of electrical power.

United States Patent Weis [54] NUCLEAR THERMIONIC GENERATOR WITH COMPOSITE PARTICLE CATHODE [72] lnventor: Arthur Martin Weis, Pittsburgh, Pa.

[73] Assignee: Nuclear Materials and Equipment Corporation, Apollo, Pa.

22 Filed: Feb. 10,1964

21 Appl.No.: 343,585

[52] US. Cl ..3l0/3, 136/202, 252/301. 1 313/54, 313/218, 313/346 [51] Int. Cl. ..G2ld 7/00 [58] Field ol'Search ..310/3; 313/54,218, 346;

[4 1 Jan. 25, 1972 [5 6] References Cited UNITED STATES PATENTS 2,556,855 6/1951 .Stutsman ..3l3/213 2,837,666 6/1958 Linder ..313/54 2,958,798 11/1960 Anton ...3 1 3/54 3,110,811 11/1963 Kramish ..3l3/54 Primary Examiner-Rodney D. Bennett, Jr. Assistant Examiner-Daniel C. Kaufman AnorneyHymen Diamond [5 7] I ABSTRACT This invention relates to the art of generating power and has particular relationship to thermionic generators of electrical power.

4 Claims, 2 Drawing Figures PAIENH-in JAHZSISTZ 3,638,051

v N 48 V R J PS 52! 133 Q HIGHLY R REFRACTORY C RADIOACTIVE CERAMIC Fig. l.

THORIATED NUCLEAR THERMIONIC GENERATOR WITI-ll COMPOSITE PARTICLE CATIIODE This invention relates to the art of generating power and has particular relationship to thermionic generators of electrical power.

Such a generator typical of the prior art includes a cylindrical cathode composed of such materials as a solid solution of zirconium carbide and uranium monocarbide in which the uranium may be highly (94 percent) enriched U An anode of a material such as stainless steel encircles the cathode in cooperative relationship. Cesium vapor is injected between the anode and the cathode. Electrons flow from the cathode to the anode because of the difference in work-function of the cathode and anode and also because of the energy imparted to l the electrons by heating the cathode. Space charge is neutralized by ionizing the cesium vapor between the anode and the cathode'to produce relatively immobile positive ions. A load connected between the anode and the cathode may be energized by the flow of the electrons.

In such prior art apparatus the flow of electrons has been low and the power derivable has been low. It is an object of this invention to provide a thermionic generator from which power of substantially higher magnitude than for prior art generators shall be derivable.

In accordance with this invention a thermionic generator is provided in which the cathode is a compacted, compressed, or otherwise formed mass of composite particles, the surface of which is maximized. Each particle consists of a core of radioactive material such as curium-242, curium244, plutonium-238 or strontium90 having deposited thereon a layer or layers or coatings of electron-emissive material. The core should be heat resistant so as to withstand the high temperature developed by the radioactivity. In accordance with an important aspect of this invention the core is a ceramic composed of oxides or carbides of curium-242, curium-244, plutonium-238 or strontium-90. The coating should also be heat resistant and in accordance with an important aspect of this invention is composed of thoriatedtungsten which is highly electron emissive. The coatings may be applied as disclosed in application Ser. No. 330,772, filed Dec. 16, 1963, to Donald E. Baker and John E. Eck. To maximize the surface of th mass the mass is provided with fins.

A mass may be formed by molding at high pressure and sintering. The composite particles are deposited in a die and high pressure and high temperature is applied to form the mass. Alternatively the mass may be formed as disclosed in application Ser. No. 250,112, filed Jan. 8, 1963 to Zalman M. Shapiro. In this case the composite particles are compressed or compacted into a mass in a form or die by application of moderate pressure and thereafter solidified by reducing a tungsten halide or the like in the mass to provide a tungsten adhesive.

The coating on the core of each composite particle is so thick that when the composite particles are compacted or compressed the coatings form a substantially continuous matrix in which the cores or grains of ceramic material are embedded. The continuous matrix is highly heat conductive and transfers the heat generated by the radioactivity of the grains effectively to the finned surface.

When the mass is heated, electrons are emitted from the thoriated tungsten coatings. Since the mass has a large external surface area, a high-electron charge is emitted from its surface.

An anode which may be composed of stainless steel is cooperative with the cathode. Between the anode and the cathode there is a cesium vapor. The vapor is ionized by the electrons providing neutralizing space charge. A load may be connected between the anode and cathode.

While a cathode of particles which are coated with thoriated tungsten constitutes an important feature of this invention, other coatings such as alkaline earth oxides, uranium carbide-zirconium carbide may be used in accordance with the broader aspects of this invention.

The novel features considered characteristic of this inventio'n are described above. For a better understanding of this invention, both as to its organization and as to its method of operation, together with additional objects and advantages thereof, reference is made to the following description, taken in connection with the accompanying drawing, in which:

FIG. I is a view in section showing a preferred embodiment of this invention; and

FIG. 2 is a view in section of a composite particle of the mass forming the cathode of the embodiment shown in FIG. I.

The apparatus shown in the drawing is a thermionic generator including a cathode C and an anode A. The cathode C and anode A are suspended from the top 5 of a dewar flask D having a hollow wall 7, the space 8 between which is evacuated. The flask D has an inlet tube 6 and an outlet tube 9 through which hot oil is circulated in and out of the flask. The flask may be cooled externally.

The cathode C is a compacted, compressed or otherwise formed mass of particles 11. Each particle 11 is composed of a core 13 of highly refractory radioactive ceramic having a coating 15 of thoriated tungsten. The ceramic may be an oxide or carbide of curium-242, curium-244, plutonium-238, strontium-90. The coating is composed of thoriated tungsten and is electron emissive.

The surface area of the cathode C is maximized. For this purpose the mass is formed with fins 17. When the cathode C is heated by the radioactivity of the cores 13, electrons are emitted from the surface of the cathode.

The cathode C has a stem 19 which may be composed of tantalum or other suitable refractory conducting material. The stem 19 may be secured to the cathode C by deposit of tungsten from a tungsten halide as taught by the above-mentioned application Ser. No. 250,l 12 or by brazing or other suitable process. The stem is screwed into a mount 21 of copper from which the cathode is suspended. A rod 23 for connecting to a load engages the copper mounting.

The anode A includes a cup 31 of a material such as stainless steel to which a fin structure 33 of a thermally conducting material such as copper is secured. The cup 31 terminates in a pocket 35 in which there is a pool 37 of cesium. The cup 31 has external fins 38 for cooling which engage the flask D.

The cup 31 has reentrant projections 39 which penetrate between the fins 17 so that the surfaces of the cathode C and anode A extend substantially parallel. The anode surface should be spaced a small distance of the order of one-eighth inch from the cathode surface.

The cup 31 is sealed by a ring 41 of generally C-section having upwardly and downwardly extending lips 43. The ring 41 is welded or brazed vacuumtight to the copper mount 21. The ring 41 is electrically insulated from the cup 31 by ring insulators 45 and 47 which are seated and sealed in the corners formed by each lip 43 and the adjacent portion of the ring 41 and in a like comer formed around the rim of a shell 48 sealed to the cup 31 and in a ring 49 sealed to the top 5.

In the making of this apparatus the cup 31 is formed of two coextensive halves which are joined in a vacuumtight joint. The cathode C, support 21, ring 41, insulators 45 and 47, and ring 48 are first assembled on the top 5 into which the tubes 6 and 9 have been sealed. This assembly is mounted in a jig and the two halves of cup 31, which have been precisely produced are inserted in the end of ring 41 with their abutting edges in engagement. The halves of cup 31 are then sealed together and into the ring 41. The sealing operation may be carried out by brazing in a furnace. The pocket 35 with tail 51 open is then sealed into the end of cup 31. The cup is exhausted through the tail 51; when a high vacuum has been achieved, the cesium-37 is introduced through the tail 51 and the tail sealed off. Cesium become liquid at 28.5 C. and may be introduced as a liquid. The wall of the dewar flask D is next sealed to the top 5. Because of the radioactivity of cathode C, the production of the apparatus must be effected with remote manipulators.

In the use of the apparatus, a load is connected between the ring 49 and the dewar flask D to which the anode A is connected through the fins 38. Hot oil is conducted through the tubes 6 and 9. The temperature of the oil is set to achieve the desired pressure of cesium vapor between the anode A and the cathode C. The radioactive material heats the cathode C producing electrons which flow through the anode A and load (not shown). The cesium vapor is ionized providing spacecharge neutralization.

While a preferred embodiment of this invention has been disclosed herein, many modifications thereof are feasible. This invention then is not to be restricted except insofar as is necessitated by the spirit of the prior art.

I claim as my invention:

1. A thermionic generator comprising a cathode consisting of a mass of composite particles each particle including a core of a radioactive material coated with a coating of thoriated tungsten, the surface of said mass being maximized, an anode spaced from said cathode and cooperative with said cathode, a vapor of an ionizable material between said anode and cathode, and connections to said anode and cathode for supplying a load.

2. A thermionic generator comprising a cathode consisting of a mass of composite particles each particle including a core of a radioactive material coated with a coating of thoriated tungsten, the surface of said mass being maximized, an anode spaced from said cathode and cooperative with said cathode, a vapor cesium between said anode and cathode, and connections to said anode and cathode for supplying a load.

3. A thermionic generator comprising a cathode consisting of a mass of composite particles each particle including a core of a radioactive material coated with a coating of an electron emissive material, the surface of said mass being maximized, an anode spaced from said cathode and cooperative with said cathode, a vapor of an ionizable material between said anode and cathode, and connections to said anode and cathode for supplying a load.

4. A thermionic generator comprising a cathode consisting of a mass of composite particles each particle including a core of a radioactive material coated with a coating of an electronemissive material, the surface of said mass being maximized, an anode spaced from said cathode and cooperative with said cathode, the surface of said anode being maximized and having a contour generally parallel to the contour of said cathode, a vapor of an ionizable material between said anode and cathode, and connections to said anode and cathode for supplying a load. 

1. A thermionic generator comprising a cathode consisting of a mass of composite particles each particle including a core of a radioactive material coated with a coating of thoriated tungsten, the surface of said mass being maximized, an anode spaced from said cathode and cooperative with said cathode, a vapor of an ionizable material between said anode and cathode, and connections to said anode and cathode for supplying a load.
 2. A thermionic generator comprising a cathode consisting of a mass of composite particles each particle including a core of a radioactive material coated with a coating of thoriated tungsten, the surface of said mass being maximized, an anode spaced from said cathode and cooperative with said cathode, a vapor cesium between said anode and cathode, and connections to said anode and cathode for supplying a load.
 3. A thermionic generator comprising a cathode consisting of a mass of composite particles each particle including a core of a radioactive material coated with a coating of an electron emissive material, the surface of said mass being maximized, an anode spaced from said cathode and cooperative with said cathode, a vapor of an ionizable material between said anode and cathode, and connections to said anode and cathode for supplying a load.
 4. A thermionic generator comprising a cathode consisting of a mass of composite particles each particle including a core of a radioactive material coated with a coating of an electron-emissive material, the surface of said mass being maximized, an anode spaced from said cathode and cooperative with said cathode, the surface of said anode being maximized and having a contour generally parallel to the contour of said cathode, a vapor of an ionizable material between said anode and cathode, and connections to said anode and cathode for supplying a load. 